RIYADH, Saudi Arabia -- Four more men allegedly linked to al-Qaida were arrested as part of a crackdown that Saudi officials launched after deadly bombings in Riyadh last week, a Western diplomat said Thursday.
The four were arrested Tuesday for their alleged ties to 19 men wanted over a weapons cache found May 6 near the site of the deadly Riyadh bombings, which occurred six days later, the diplomat said on condition of anonymity.
Saudi Arabia launched a sweeping crackdown on extremists after the suicide attacks May 12 on the three compounds in Riyadh that killed 34 people, including eight Americans and the nine attackers.
Saudi officials said Thursday that about 100 people have been detained so far.
The government has said the 19 people wanted for questioning about the cache were believed to be receiving orders directly from Osama bin Laden.
They may have been planning to use the seized weapons to attack the Saudi royal family and American and British interests.
Also Thursday, Saudi security officials said three Moroccan citizens arrested Monday on suspected links to al-Qaida planned to hijack a plane in the southwestern Saudi port of Jiddah and crash it into a building or other landmark.
The men had planned to leave behind a one-page testament saying they were fighting against American involvement in Iraq, the security officials said on condition of anonymity.
The Saudi officials also said they had confiscated weapons in Jizan, near Saudi Arabia's long and porous border with Yemen, and found evidence of terrorist training sites in the holy city of Medina and on farms outside Riyadh.
Saudi Arabia says it is trying to avert more violence, but cannot guarantee attacks have ended.
"The Saudis are working very, very aggressively throughout the kingdom," the Western diplomat said.
Victor Edan, from Batangas, Philippines, said the Riyadh attacks, which killed several Filipinos, made him wonder whether he should stay in Saudi Arabia.
"I don't go out as much as I used to and I am really scared now," said Edan, 36, one of thousands of Filipinos living and working in the kingdom. "I am constantly thinking whether I should stay or not."
Britain, Germany and Italy joined the United States in closing diplomatic offices in Saudi Arabia for at least a few days starting Wednesday because of terror fears.
The pan-Arab satellite station al-Jazeera released an audiotape Wednesday in which the purported voice of bin Laden's top lieutenant, Ayman al-Zawahri, called on Muslims to "consider your 19 brothers who attacked America in Washington and New York with their planes as an example."
The 19 Sept. 11 hijackers included 15 Saudis.
In Washington, a U.S. official, speaking on condition of anonymity, said it was plausible that the speaker was al-Zawahri but a thorough analysis was necessary to be certain.